Apple
Sooty Blotch of Apple
Phyllachora pomigena
Fungus
In a Nutshell
- Dark green to black sooty fungal growth on the surface of the fruit.
- Circular to irregular individual patches.
Can also be found in
Apple
Symptoms
There are brown to dull black sooty blotches with an irregularly shaped outline on the surface of the fruit, which may be 5 mm in diameter or larger. The blotches may come together to cover the entire fruit. Sooty blotch appears as sooty or cloudy blotches on the surface of the fruit. The blotches are olive green with an indefinite outline. The blotches are usually one fourth of an inch in diameter or larger and may coalesce to cover much of the fruit. The 'smudge' appearance results from the presence of hundreds of minute, dark pycnidia that are interconnected by a mass of loose, interwoven dark hyphae. The sooty blotch fungus is generally restricted to the outer surface of the cuticle. In rare cases, the hyphae penetrate between the epidermal cell walls and the cuticle.
Recommendations
Organic Control
Coconut soap treatments during summer can reduce the disease incidence slightly.
Chemical Control
Always consider an integrated approach with preventive measures together with biological treatments if available. Sprays of strobilurin fungicide, kresxim methyl or trifloxystrobin have been evaluated to control sooty blotch. and thiophanate-methyl. Captan, Inspire Super and other pre-mixes are believed to provide a good control but are not quite as effective. Spray Mancozeb 75% WG (3G/L) of water and use spray fluid of 10 L of spray fluid/tree.
What caused it?
The disease is caused by Phylachora pomigena (several unrelated fungi). Spores of the fungi are windblown into the plantation. The disease outbreaks are favored by long continuous periods of above normal summer temperatures with frequent rainfall and high humidity. The fungal growth may leave a discoloration behind. . It affects the leaves, twigs and fruits of a wide range of woody and herbaceous plants. Spores are produced in spring and early summer.
Preventive Measures
- Remove alternate hosts such as brambles from the orchard and surrounding hedgerows.
- Prune trees in summer to open up tree canopy and facilitate air movement, and the drying of fruit after rainfall.
- Thin out trees to separate fruit clusters and also prevent the disease incidence.
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